This invention relates to a hydraulic pressure amplifier or intensifier which receives pressure fluid from a low pressure pump and increases the pressure of the fluid automatically to a desired magnitude before delivering the fluid to a utilization device. One specific type of utilization device which the amplifier may serve is a single-acting hydraulic actuator having a rod which is advanced in one direction when pressure fluid is admitted into one end of a cylinder. When the pressure fluid is released from the cylinder, a spring returns the rod in the opposite direction.